Production of alumina



Hydrogen A um inum Separator G. L. HERVERT ET AL 2,355,275

PRODUCTION OF ALUMINA Filed July 8, 1955 Unreacfea' Aluminum Fines Mr I \f" I 4 /5 M Q) a. Q Q F: u

x //V V E N TORS: 2 George L. Hervert g y Harman 5. Bloch Q) k zfm J I Arron/vars,-

United States Patent 10 PRODUCTION OF ALUMINA George L. Hervert, V Downers Grove, and Herman S. Bloch, Chicago, Ill., assiguors to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Application July 8, 1955, Serial No. 520,802

5 Claims. (Cl. 23-143) -Thisapplication is a continuation-in-part of our copending application Serial. No. 315,414, filed October 17, 1952, now abandoned.

. This invention relates to the preparation of alumina and more specifically to a method of preparing alumina by the interaction of water and metallic aluminum in the presence of organic catalysts.

Alumina, either as the hydrate or the anhydrous form as aluminum oxide is widely used in the petroleum and many other branches of chemical industry. It has been employed in the petroleum industry as a catalyst for hydrocarbon conversion processes, as a support for catalytically active materials to be used in hydrocarbon conversion processes, and as a dehydrating agent. It is widely used in other fields ofchemical industry for the same purposes. The activated forms which are considered to be merely modifications of aluminum oxide and its hydrates are especially known for their pro,- nounced catalytic activity and adsorptive capacity. The use of alumina as a refractory is also Well known. Alumina in the form of corundum has been found suitable 2,855,275 .Piatented Oct. 7, 1958 Gamma-Al O -H o or Bohmite may be prepared in a variety of ways, one of the simplest being to add ammonium hydroxide to a water solution of aluminum chloride. The material originally precipitated is thought to be an amorphous alumina flock which rapidly grows in crystal size yielding crystalline Bohmite. Aging the Bohmite in ammonium hydroxide solution transforms the Btihmite first to meta-stable Bayerite and finally to the stable Gibbsite.

Alpha-Al O -H o or Diaspore occurs abundantly in nature. I i

In the specification and claims the word alumina will mean one or more of these various modifications, either as anhydrous alumina or alumina hydrate or aluminum hydroxide unless otherwise specifically noted.

By varying the conditions of the process of this invention it will be shown that some of the various modifications of alumina as hereinbefore described may be obtained.

The usual commercial method of producing alumina is by purifying ores in which the oxide is present. Another method is by the precipitation of aluminum hydroxide from its salts, for example, by the addition of ammonia to an aqueous solution of aluminum sulfate. However, the physical form of the product produced in -our process is much superior since it is crystalline and easily filterable, while the precipitated aluminum hydroxide is a gel that is filtered with difiiculty.

We have now discovered and our invention broadly comprises an improved method for preparing alumina by reacting aluminum with water under specific conditions for use in the manufacture of certain types of refractory and ceramic materials. High purity alumina is also used medicinally. In other uses alumina is mixed or blended with other components to produce substances of modified properties.

In one modification of the invention the alumina pro- I duced under the conditions of our invention is in an ex-- tremely fine state of division and requires no grinding to render it impalpable, nevertheless it is relatively easily filterable and may thus be readily separated from the liquid in which it is formed so that the latter may be reused. The alumina in an extremely finely divided form, that is, an impalpable powder, is especially suitable for cosmetics, medicinals, fine abrasives, or agricultural or military dusting purposes.

- It is an object of our invention to provide a newproc ess for the production of alumina and further to produce stable at temperatures over about 1800 F. 1

Gamma-alumina is very stable but changes to alpha alumina at temperatures above about 1800 F. Epsilon-alumina is the alumina'formed in thin films on the surface of metallic aluminum during oxidation by dry or wet air or oxygen.

Gamma-Al O -3H O or Gibbsite is prepared by aging Bohmite in a cold basic solution.

Alpha-Al O -3H O or Bayerite is also formed by aging Bohmite in a cold basic solution but is unstable and gradually is transformed into Gibbsite.

and in the presence of certain water soluble organic catalytic substances. Hydrogen in a very pure state is produced as a by-product of this reaction.

Itis recognized that theart teaches that alumina is formed on the surface of aluminum upon exposure to dry or wet air or oxygen; however, it is always referred to as a protective coating of alumina which prevents the aluminum metal under this coating from being converted to the oxide. Our invention, however, is such that a substantial amount, and in the more desirable aspect, the entire amount of aluminum is converted to the oxide and is separated as such, that is substantially free from aluminum metal. In the prior art the protective coating is taught to be of a tenacious nature, in that it adheres rigidly to the aluminum metal, while in our invention alumina is formed in a state that is easily separated from the reactants. In the preferred embodiments of our invention all of the aluminum is converted to the hydrated oxide and it is only necessary to separate water and catalyst therefrom which may be done by appropriate filtering or heating steps. In other modes of operation where all of the aluminum is not converted to the oxide, the two solids occur substantially as distinct separate solids which do not adhere and are not attached to each other to any appreciable extent and may thus be separated by any satisfactory means, such as'centrifugal separation, flotation, and the like. It is not necessary and, in fact, it is undesirable that the separation be effected by some cutting means, suchas scraping or tumbling to remove the oxide from the surface of the metal since under the condition of operation of our invention alumina is present, distinct and separate from the aluminum metal from which it is formed.

The aluminum to be used in our process can be any commercially available aluminum although if a high purity alumina product is desired it is preferable to start with high purity aluminum. It is also within the scope of this invention to use aluminum alloys, however, since the present process will produce a very pure alumina, it is a preferred embodiment of the present invention to aluminum may beused, or aluminum t-urnings, or'granu" lated aluminum. Aluminum pellets prepared by dropping molten aluminum into water-havelikewise-preven to be very satisfactory for producing alumina by the proc-} ess of our invention, those pellets below about an ineh in average diameter beingpreferred.

One embodiment of the present invention comprises agitating the aluminum and water and catalytic substances sufiiciently so that the reaction to produce alumina-pro ceeds at a desirable rate. The-reaction velocity is dependent upon the temperature of the reactants, the degree of subdivision of the aluminum, andthe-degree'ofagitation given the mixture. Thusa. reaction that proceeds slowly at a temperature of 212 F. with only a mild agitation or shaking of the mixture will proceed very rapidly if the mixtureis vigorously agitated. At a temperature of- 572 F., on the other hand, the reaction proceeds relatively rapidlyeveniwith a mild degree'of'agitation. However, if the mixture issubjected to vigorous. agitation, the time necessary for complete reaction is substantially de' creased.

A preferredembodiment of the'present invention relates to the process for producing hydrated alumina which comprises reacting aluminum with water in the presence of certain, water soluble organic catalytic substances, agitating the mixture to form alumina, maintaining apressuresufficient to keep. at least a portion of the water in the liquid phase and separatelyrecovering alumina there-- from.

It is a desirable feature of the present invention that liquid water be present and it is thus necessary When. temperatures above the boiling point are. employed to effect the reaction under sufiicient pressure to maintain a liquid phase ofwater.

ture being that temperature above which a gas cannot be liquefied. by pressure alone. It is desirable to useliquid water since it is much easier to have intimate contact and especially mixing between the aluminum and water accomplished'if there'- is a liquid phase. However, the reaction will also proceed if the water is present in the vapor phase, especially at superatmospheric pressures, and while it is a desired feature to keep water in the liquid phase, it is not'at all a limitingfeaturei Experiments conducted at temperatures near the critical ternperature at pressures sufiicient to maintain water in the liquid phase have been entirely successful and the reaction proceeds at a very rapid rate. Also; experiments conducted at temperatures near the critical temperature and at pressures insuflicient to maintain water in-the liquid phase have been entirely successful. From a practical standpoint, the upper temperature can be' limited to about 850 F. since temperatures above this cause excessive decomposition of most' of the efiective organic nitrogen-base activators.

In another embodiment the presentinventionrelates to a process for producing hydrated alumina which com-*- prises reacting aluminum with waterin the presenceof a non-metallic organic base to form' alumina and sepa'- rately recovering alumina therefrom.

In a specific embodiment the-present'invention relates to a process for producing alumina which comprises reacting aluminum with water in the presence of a water soluble organic nitrogen base toform aluminaand separating the resultant alumina fromthereaction'mixture.

In another specific embodiment the present invention relates to a process for producing alumina which comprises reacting aluminum with water inthe presence of The critical temperature of" water is 705L2 F.; the definition of the critical tempera--- ethanolamine to form alumina and separately recovering alumina therefrom.

In a further embodiment the present invention relates to a process for producing alumina which comprises reacting metallic aluminum at a temperature of from about 30 F. to about 705 F. with liquid water having a water soluble organic nitrogen-containing base dissolved therein.

The water soluble organic nitrogen base used in this reaction acts as an accelerant to speed the reaction of aluminum with. water in order to form the desired alumina. We have discovered, and our invention is based on the-discovery, that water soluble organic nitrogen bases are catalysts for the reaction between aluminum and water to form alumina. It is the catalytic properties not merely the physical or chemical properties, of the organic bases which causes them to be catalysts for this reaction. The exact reason why the water soluble organic nitrogen bases are catalysts for this specific reason is not known, and the discovery was unexpected. Wherethebase used inthis process isof such a naturethat it reacts or promotes reaction with walls of an ordinary reaction vesselit'i'spreferred', of course, that the reaction vessel be constructed of material inert to the reactants in order that corrosion and contamination of the products may be avoided.

A preferred step of the present invention is the reaction of aluminum with water in the presence of a water soluble nitrogen-containing organic base, such as ethanol amine. When awater soluble nitrogen-containing or-- ganic' base is used as a catalyst inthis-reaction, the reac-- tion will proceed at amuch lower temperature than if these bases are absent. For example, if 18- grams of aluminum and ZOOgrams of distilled water are placed in a pressure autoclave and the reaction mixture'is heated to 200 F., only a very small amount of reaction is noticeablewithin 24' hours; however, if a catalytic amount of monoethanolamine is introduced. the reaction will have been substantially completed. in 6 hours.

Further, in the presence of the water soluble nitrogen-- containing organicbases, aluminum alloys which are inert'to theaction of water alone even at high temperatures (such as 28 aluminum containing-1% Fe, 0.2% Mn, 0.1% Cu',0'.2% Si, 0.05% Ga, 0.03% Mg, and 0.008% Ti) react readily at relatively mild temperatures.

Since the water-soluble organic base acts as an accelerant' or catalyst it is preferably used in very low concentrations. The water soluble organic nitrogen base. need not be completely soluble in water but it need only be soluble to the extent that it is needed as a catalyst. For example if only 2% by weight of'a specific organic nitrm gen-containing base is' necessaryto catalyze the reaction, it is only necessary for the base to bewater soluble to the extent of 2%. The base, however, must be water soluble at the reaction temperature. We have found that there is a range of concentrations in which the base exhibits maximum activity. For example, we have found that concentrations of monoethanolamine used as a catalyst within the range of from about 4% to about 20% have the highest catalytic effect and concentrations lesser or greater than these do not have as great a catalytic effect. Similarly, with n-butylene maximum reaction velocity leading to substantially complete conversion of the aluminum in a minimum time, occurs with amine concentrations of about 4% to about 23%. Any amount of a base, used as an accelerant or' catalyst herein mentioned will be a catalytic amount or referred to. as a catalytic amount. The concentration of the catalystin the water-catalyst solution' will" usually be within the range of from about 0.05% to about 50% by weight.

The catalyst may consist of water solublev nitrogencontaining organic bases such as:

(1') Primary, secondary, and tertiary alkyl'amines', as for example, ethylamine, diethylamine and triethylamine,. butylamine.

(2), The alkanolamines, for examplethe ethanolamines,.

- such as monoethanolamine, diethanolamine and triethanolamine.

(3) Aryl-alkyl amines (primary, secondary and tertiary) such as benzylamine, methylaniline and dimethylaniline.

(4) Pyridine and its homologs, such as the picolines, lutidines and collidines.

(5) Piperidine and its homologs.

In general, we have found that the organic nitrogeneous bases fall roughly into three classes: those having, in aqueous solution, ionization constants equal to or greater than and exhibiting pH values (for 2-25% solutions) above about 12, which are highly active catalysts for dissolving aluminum; those having ionization constants equal to or below about 10- and exhibiting pH values of less than about 11, which are poor catalysts; and those exhibiting intermediate pH values (11 to 12) and having intermediate ionization constants (10" to 10-), which are fair catalysts.

It is our belief, although we do not intend the scope of this invention to be limited by this theory, that the nitrogen bases catalyze the reaction of aluminum with water by continuously dissolving the protective aluminum oxide film thereby exposing fresh aluminum surface for reaction. It is possible, for example, that the oxide film is removed by the (formation of aluminum-nitrogen base complexes which are sufliciently soluble to be carried into the aqueous phase wherein alumina is precipitated from the complex and the nitrogen base regenerated for further use.

As hereinbefore stated the organic nitrogen-containing base must be water soluble, but need only be water soluble to the extent that it is needed as a catalyst at the reaction conditions. It may, therefore, be considered that the aluminum is reacted with water having an organic nitrogencontaining base dissolved therein or it may be stated that the aluminum is reacted with an aqueous solution of an organic nitrogen base. The word solution is intentionally used so as to indicate that the organic base is soluble in the water to the extent required. I Several of the advantages of our process have hereinbefore been mentioned. The process also has the advantage of introducing only volatile materials into the reaction mixture and these may easily be removed from the product alumina by heating or oxidation. The organic nitrogen-containing bases also have the advantage of having a wide variety ofboiling points. Therefore, when it is desired to conduct the alumina-water reaction at a high temperature an organic nitrogen-containing base with a high boiling point may be used. This is a definite advantage over other processes in which a volatile catalyst is used, since in our process a'high concentration of the organic nitrogen base may more easily be maintained in the liquid phase.

Much has already been made of the fact that it is preferable to use a liquid phase of water and, therefore, the preferred upper limit of temperature that the reaction may proceed at is the critical temperature of water of about 705 F. The reaction requires increasingly longer periods of time as the temperature of the reaction is decreased and where the time of the reaction is not important it is possible to effect the reaction at temperatures down to the freezing point of the water and catalyst solution, that is, about 32 F. or lower, although the reaction is quite slow at such low temperatures. Thus the temperature range in which the reaction between aluminum and water in the presence of a catalyst is effected is from about 32 F. to about 850 F.

Within the range of temperatures in which the reaction may be effected the alumina is produced in various modifications. In the lower range of temperatures, for example, from about 32 F. to about 160 F. the alumina is produced in an extremely finely divided form that is, .the alumina is produced in this form directly without the need of attrition or grinding. To obtain this finely di vided alumina, or impalpable powder directly, the relic tion is effected at relatively low temperatures which necessitates relatively long reaction periods. The preferred upper temperature limit is about F., however, temperatures above this may be used with the understanding that if the reaction is effected at temperatures above about 160 F. alumina particles will be formed in an increasingly larger average crystalline size. The reaction requires increasingly longer periods of time as the temperature of the reaction is decreased and where the time of the reaction is not important it is possible to eifect the reaction at temperatures down to the freezing point of water and catalyst solution, that is, about 30 F. Thus the preferred range of temperatures in which the reaction between aluminum and water in the presence of a catalyst is effected to produce the most finely divided form of alumina is from about 30 F. to about 160 F. The alumina produced in this reaction is further characterized as being Gibbsite. An analysis of the alumina product formed at 400 F. shows that the product is chiefly Gibbsite, however, traces of Bohmite, a modificaa tion of alumina, are evidenced. As the temperature of the reaction is increased in excess of 400 F. the percent of Bohmite in the product is accordingly increased, and at a temperature of approximately 650 F. the product of the reaction between aluminum and water in the presence of a catalyst is analyzed as being Bohmite. The temperature at which the reaction is carried out also affects the size vof the aluminia crystals. The reaction between aluminum and water at high temperatures will produce larger crystals which after drying appear to be rough enough to use as an abrasive. The amount of organic nitrogen base activator present also affects the crystalline size, larger average particle sizes being obtained with lower concentrations of activator. Further, particle size distribution data on A1 0 produced [from themonoethanolamine catalyzed reaction at 212 F. indicate that smaller particles of alumina are produced at higher amine concentrations.

The reaction may be eifectcd in any suitable type of equipment wherein the reactants are subjected to agitation and preferably to vigorous stirring. The operation may be carried out in continuous or batch-wise fashion. When temperatures above the boiling point of water are employed and the reaction is performed with water in the liquid phase it is, of course, necessary that the-reaction vessel be capable of withstanding pressures sufficient to maintain a liquid phase of water. In small scale production of alumina by this process a rotating pressure autoclave is satisfactory. When the temperatures employed are below the boiling point of water the reaction may be eifected in ordinary open equipment, in which a means is provided for the safe escape of hydrogen and for vigorous stirring or agitation of the reagents. It is, however, necessary that the process equipment be constructed of such materials that they are not atfected by water or aluminum and/or the catalysts used so that undesirable elements are not introduced into the desired alumina product. However, if the presence of these foreign substances is not objectionable the above precautions need not be adhered to. Hydrogen is produced as a by-product of the reaction and a means of venting must be provided if the pressure build-up caused by the production of this hydrogen is to be avoided. If the equipment will withstand this additional pressure, however, it is not necessary to vent the hydrogen continuously.

The figure of the accompanying diagrammatic flow drawing illustrates a particular method for continuously conducting the process which incorporates several specific embodiments of the invention. For simplification, equipment such as valves, pumps, and similar appurtenances have been omitted in the drawing. These are well known and are not essential to the understanding of the invention.

Referring to the drawing, aluminum in the form of chips .or pellets is passed through line 1 Einto reactor 2 which is provided with a stirring or agitating device 3 and a means .of :yenting hydrogen .4. Water at .approxi mately 212 F. plus a promoter are introduced into reactor 2 through line '5. The reaction between aluminum and water is allowed to proceed in reactor 2 until the aluminum is essentially entirely converted to alumin-a, traces of aluminum fines and .water form a slurry in the reactor which is withdrawn through line 6. The slurry in line 6 is passed into .separator 7 which is provided with a stirring device .8 which provides sufiicient agitation .to aid insuspending the alumina but allows the unreacted aluminum fines to settle irom the slurry to the bottom of the separator. The aluminum fines are periodically withdrawn .through line 10 and are passed through valve 11 and line 12 to .be reclaimed and may be again introduced into ifiafitor 2. The alumina slurry in separator 7 is withdrawn through line 9 and the slurry is introduced into filter 13. Filter 13 may be any suitable filtering meanssuch asa continuous rotaryfilter-or it may be any usual commercial batch filter that may be found suitable for this process. The alumina is withdrawn from the filter through line 14 and may be subjected to further treatment .such as washing to remove traces of the promoter or thealumina may be directly dried and calcined for any of the various uses hereinbefore mentioned. The water and promoter'from filter 13 are removed through line 15 and are joined by a make-up water plus promoter stream in line 16 after which the combined stream is passed through heat exchanger '17 and into line 5. In heat exchanger 17 the water plus promoter are raised to the desired reaction temperature. If it is preferred to effect the ,reaction at temperatures above the normal boiling point of water-it is necessary that reactor 2 .beconstructed. so as to withstand process pressures at least suflicient to maintain a liquid phase. In these modes of high temperature andpressure operation it may be desirable to substitute a direct heater for heat exchanger 17.

The precipitated alumina formed in our reaction need merely be filtered from the water-organic nitrogen base mixture and water washed to be-ready for use; in many cases, especially where a subsequent calci-nation is involvedin the use of the alumina,even the waterlwashing is unnecessary since no foreign non-volatile materials are introduced during .the preparation of the alumina; the absence of foreign metals in the product alumina is. in fact, a feature of this method of preparation. The organic nitrogen base is not consumed in the reaction and the filtrate from the alumina may, therefore, be reused [for further reaction withaluminum.

The following examples are given to illustrate our invention but are not given for the purpose of unduly limiting the generally broad scope of said invention.

Example I 18 grams of aluminum pellets (99.9+% pure) of to A3 inch diameter and 200 grams of distilled water were placed in an Ipatieff type autoclave of 850 ml. capacity which was fitted with a-Pyrex liner. Theautoclave was then sealed and flushed with nitrogen after which it was heated to 392 F. The reaction was allowed to continue for,24 hours after which time an inspection and analysis showed that only a small amount of the aluminum reacted with water to form alumina. The alumina product was dried at 230 F. for one hour and an analysis showed that the product was Gibbsite (gamma Al O .3H O). The results showthatat a temperature of 392 F. and conditions as outline above, the reaction is extremely slow and would not be :an attractive process for producing alumina.

Example II 18 grams of'aluminum pellets of 99.9+% purity and CPI Example 111 20. g am Q disti wat r a 18 am 9 alum num chips apn ex m t y ,46 inch wid 4 nc .1Q d 4 n h thib a d p -9.+% Purity re B sed i 1 liter flask which was provided with a six ,bladehigh speed stirrer. The aluminum and the water were'lgept at room temperature (approximately F.) for a period of 15 days and atthe end .of this period only a small amount of alumina was noticed in the reaction vessel; the bulk of the aluminum was unchanged.

Example IV 18 grams of aluminumchips of 99.9+% purity and 200 grams of a.6% solutionofethanolamine were placed in an Ipatieif type autoclave of 850 ml. capacity which was fitted with ,a Pyrex liner. The autoclave was then sealed and flushed with nitrogen at atmospheric pressure after which it was heated to F. and the reaction was allowed to proceed for 24 hours. A .yieldgf 75% o G hhsite su tsd- Example V 9 a s ,1i. .ti1 s wate grams o thanp am ne a 8 g ant a uminu e p c i a .1 liter Pyrex fl whic a .fi t d wit a i hl d high speed Pyrex stirrer. The ,mixing was continued atroom temperature (which varied-from 75 F. to .85 .F.) ,for 285 hours. An inspection of the product showed that all h in .w scqnve te t mi The P oduc was filtered and then dried at 230 F. for two hours, yielding an impalpahle powder comprising extremely finely divided crystals of alumina which was further characterized as being Gibbsite am a Al O -3H Q). The average particle sizeof this product was vabout 3 microns.

Ex ample Vl In tests conducted for .-six hours at -212 F. in a Pyrex flask fitted with a'high-speed stirrer, 6% aqueous solutions of the following nitrogen bases caused substantially complete conversion of pure aluminum metal to Gibbsite: 'triethylamine, diethylene triamine, piperidine, monobutylamine, ethanolarnine. Similar tests showed partial reaction of the aluminum in the presence of the following catalysts: dibutylamine, morpholine, diethanolamine.

From the foregoing specification it can be seen that we have provided a new method for the production of alumina. The foregoing illustration was to show the advantages of a particular flow of the hereindisclosed process. Many other illustrations differing in minor details but within the scope of this invention can be cited, 'hence the invention should not be restricted except by the terms or the spirit of the claims.

We claim as our invention:

1. Aproc-ess for producingalumina which comprises reacting metallic aluminum at a temperature of from about 30 F. to about 705 F. with liquid water'having a catalytic amount of a water soluble alkanolamine dissolved therein for a timesuflicient to react a substantial portion, .at'least, of the aluminum with the-water, and separating the resultant alumina from the reaction mixtrue.

2. The process of claim 1 :further characterized in thatsaid temperature is in the range of 'fromabout30 F. to about 160 F. whereby the alumina is produced in finely divided form.

3. The process of claim 1 further characterized in that said temperature is in the range of from about 30 F. to about 400 F. whereby the alumina is produced in the form of Gibbsite.

4. The process of claim 1 further characterized in that said temperature is in excess of 400 F. but not above about 850 F. whereby the alumina is produced in the form of Bohmite.

5. The process of claim 1 further characterized in A that said alkanolamine is ethanolamine.

10 pages 142, 220.

Evans: The Corrosion of Metals, 2nd Edition, published by Edward Arnold and Co., 1926, page 111. 

1. A PROCESS FOR PRODUCING ALUMINA WHICH COMPRISES REACTING METALLIC ALUMINUM AT A TEMPERATURE OF FROM ABOUT 30*F. TO ABOUT 705*F. WITH LIQUID WATER HAVING A CATALYTIC AMOUNT OF A WATER SOLUBLE ALKANOLAMINE DISSOLVED THEREIN, FOR A TIME SUFFICIENT TO REACT A SUBSTANTIAL PORTION, AT LEAST, OF THE ALUMINUM WITH THE WATER, AND SEPARATING THE RESULTANT ALUMINA FROM THE REACTION MIXTURE. 